1. Field of the Invention
The present invention relates to a multi-stepped pulley around which a plurality of belts are wound, more particularly relates to one which is effective when used for a pulley for transferring a drive force of an engine mounted in a vehicle to a compressor of a vehicular refrigerating cycle, and to a method and apparatus for manufacturing the same.
2. Description of the Related Art
As the shape of the multi-stepped pulley of the related art used for driving the compressor of a vehicular refrigerating cycle, there is for example well known the one shown in FIG. 1.
Specifically, a plurality of rims over which so-called "poly-V-belts" are wound, that is, a first rim 111 and a second rim 121, are connected coaxially. A web 123 is provided on an end portion of one of the rims (right side end portion of the second rim 121 in FIG. 1). This multi-stepped pulley is held and fixed by welding the inward circumferential side of the web 123 to a rotating body such as a rotor 140.
In such a multi-stepped pulley, however, in addition to a second bending stress resulting from a tension acting upon the belt wound over the second rim 121, a first bending stress resulting from a tension acting upon the belt wound over the first rim 111 is generated at the web 123 and a connection portion between the web 123 and the second rim 121. For this reason, stress easily concentrates at the web 123 and the connection portion between the web and the second rim 121 in the multi-stepped pulley, so it is necessary to increase the mechanical strength of this portion.
However, there is a problem in that if simply making the thickness of the web 123 and the connection portion between the web 123 and the second rim 121 thicker in order to increase the mechanical strength, the mass of the multi-stepped pulley is increased and the manufacturing cost rises due to the increase of the material used.
Further, as a method of manufacturing of general multi-stepped pulley, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-132238, thre has been known a method of forming a plurality of rims by "slotting" a substantially disk-shaped metal material of the multi-stepped pulley.
In the method of forming a plurality of rims by "slotting", that is, cutting open the material by a roller blade, however, there is large abrasion of the front end of the slotting roller for slotting the multi-stepped pulley material, so there is a problem of a short service life of the slotting roller.